Means for bathing workpieces in a controlled atmosphere



Feb. 16, 1943.

A. w. MACHLET I MEANS FOR BATHING WORKPIECES IN A CONTROLLED ATMOSPHERE2 She ets-Sheet 1 Filed March 4, 1941 INVENTOR av Wi'm lllllllll IIIIIIIL ATTORNEY Patented Feb. 16, 1943 RIEANS FOR BATHING WORKPIECES IN ACONTROLLED ATMOSPHERE Adolph Machlet, Elizabeth, N. J.

Application March 4, 1941, Serial No. 381,638

8 Claims.

This invention relates to improvements in apparatus useful in heattreating processes for ferrous and non-ferrous articles and is concernedmore particularly with an improved furnace and means for maintaining thework placed therein for treatment isolated from the atmosphere of thefurnace oven and simultaneously bathed in a controlled atmosphere whichmay be kept continually in a state of motion.

A primary aim of the invention is to insure continuous movement as wellas uniformity in the rate of flow of a given treating atmosphere aboutthe work to be heated, without regard to the atmosphere that existswithin the furnace proper, to the end that substantially the entiresurface areas of the workpieces will be reached by the moving currentsof the selected medium during the treating process, to the exclusion ofair or gases from other sources.

Afurther aim of the invention is to effect substantial uniformity in therate of circulation of the atmosphere about and in contact with theworkpieces by an improved method and means that further insurescirculation of a medium preheated to a temperature that does not chillthe work when the medium employed is first brought into contact with theworkpieces. And by way of an additional refinement the invention aims toextract a substantial portion of the heat units from the circulatingmedium as it is conducted away from the workpieces and to utiliz theheat units so extracted in the warming of the incoming supply of newgases before or as they are introduced into the zone or vicinity of theworkpieces.

A further objective of the invention is to render available a closedcirculating system for a furnace that may, when the occasion requires,have the direction of flow of the atmosphere in the immediate vicinityof the workpieces reversed at will, and notwithstanding such reversalsin movement, to effect a heating of the atmosphere before or as it flowsinto the region adjacentthe work to be treated.

Still another object of the invention is to provide a furnace with acirculating system that may be maintained under appropriate pressure andwhich is closed to the direct atmosphere of the heating means and/orheating chamber of the furnace and which is efficient in operation andeconomical in its consumption of treating gas-es, and a system thatrequires relatively few parts each of simple design and inexpensiv'etomanufacture and install.

In attaining the objectives of this invention, it is proposed to supportthe workpieces or pieces to be treated in a relatively tall normallyclosed retort or work chamber. Preferably the retort is cylindrical andis spaced from the walls of the heating chamber of the furnace to allowcirculation of heat therearound. Located preferably at the center of theretort, an open topped tube or tubular chamber is constructed thatcommunicates at its lower end with a conduit that extends through thebottom of the retort and also through the bottom of the furnace proper.A removable cover normally overlays and seals the top of the chambercontaining the work but which leaves sufficient space between theunderside of the cover and the upper end .of the central tubular duct topermit free flow of air or gases through the duct to or from the workchamber proper.

At the lower end of the work chamber, a second conduit communicatestherewith and projects through the bottom thereof and also through thefurnace wall. This second conduit has its open end within the workchamber and overlaid by a system or series of baffle plates, also withinthe work chamber, that serve to impede the flow of the atmosphere to orfrom the conduit to the interior of the retort iwork chamber.

Preferably the two tubes or conduits just mentioned telescope oneanother beginning at a region within the retort to a region somedistance beyond the outer wall of the furnace proper where they connectrespectively with a source of supply of treating gas and a chimney orother circulating apparatus.

With such an apparatus, the treating gas or gas mixture is caused toflow through one of the tubes into the closed retort at one end thereof,and is gradually forced through and about the work that may be stackedtherein, and is with drawn from the other end of the retort and awayfrom the furnace through the other concentric tube. During thecirculating cycle, the

system of baffles at the lower end of the retort impede the flow of thegases from the supply conduit associated therewith and effectivelyprevent the stream of entering gases from blastingthe workpieces.Simultaneously, the baffle plates which become heated along with theretort and work therein, serve as a preheating means for the gases asand when the treating gases are introduced and dispersed into the closedwork chamber at the bottom. When the system is so operated, the hotgases leaving the top, portion of the retort, fiow downward through thecentral tube and as the incoming and outgoing conduits telescope eachother for a substantial distance, the outgoing stream of hot gases givesup a large part of its heat to the incoming and relatively cool streamof treating gases. In this way, the entering treating gases becomeheated before they are caused to contact the work, first during theirpassage through the concentrically arranged tubes and again during theirfiow through the labyrinth of passageways afforded by the baflle plates.

When the circulating system is operated in the reverse direction, theincoming gases are again heated during their flow through theconcentrically arranged tubes and again during their flow through theconduit that extends centrally of the work chamber to the upper regionsthereof. This central tube will, of course, become heated indirectlythroughout its length, and to increase its effectiveness as a heater forincoming gases, it may be provided with inwardly projecting fins orbafiles. Such devices further serve as a flow retarding medium so thatagain the incoming gases do not blast the workpieces. The baflies at thelower end of the retort, which in this instance will be the dischargingend, also function as a flow retarding medium, and the two bafilesystems cooperate to maintain the interior of the retort free of swiftlyflowing gas streams and otherwise insure uniform distribution of theatmosphere about the work.

A preferred apparatus for effecting movement of the gases through theretort consists in connecting the supply and exhaust gas conduits toopposite sides of a blower and therewith insure continuous forcedcirculation of the atmosphere about the work enclosed in the retort.With such a closed system, improved results are attained with the use ofa pressure regulating device in the system, together with means forintroducing a fresh quantity of treating gas to compensate for the gasesconsumed or vented during the heating and treating process.

Alternatively, the retort exhaust conduit may connect directly with thestack or chimney of the shop and the current or draft effected may beutilized to provide the means for circulating the atmosphere within theretort about the work. In any circulating arrangement, however, a reversing valve may be connected in the supply and discharge conduits leadingto the retort wherewith the operator may conveniently reverse thedirection of movement of the gases through the retort, i. e., to causethe new supply to enter the retort at the bottom and to be drawn off atthe top, or reversely.

Other objects and advantages will be in part indicated in the followingdescription and in part rendered apparent therefrom in connection withthe annexed drawings.

To enable others skilled in the art so fully to apprehend the underlyingfeatures hereof that they may embody the same in the various wayscontemplated by this invention, drawings depicting a preferred typicalconstruction have been annexed as a part of this disclosure and, in suchdrawings, like characters of reference denote corresponding partsthroughout all the views, of which:

Figure 1 is a sectional view of a furnace embodying the principles ofthis invention.

Fig. 2 is a detail view of a furnace with a more simplified form ofmechanism for obtaining circulation of the atmosphere in a work chamber.

Fig. 3 is a fragmentary view of a bafile system for a conduit.

Fig. 4 is a sectional view illustrating a construction whereby the workbaskets themselves are constructed as to form the central tube or ductwhen assembled within the work chamber.

Fig. 5 is a detail view of a work basket interlocking means, and Fig. 6a tool for manipulating the baskets.

Referring more particularly to the apparatus illustrated in Fig. 1, thefurnace is composed of side walls Ill, a bottom wall Ii, and a removablecover member I 2. The chamber I3 thereof may be heated in any well knownmanner, such as gas, oil, electricity, and. the heaters are in thisinstance represented by the numeral l4.

A substantially hollow container or retort I5 is lowered into the workchamber and rests upon short legs IS. The retort also has a removablecover I! which normally is sealed around its rim by means of theinterdigitating rim flanges l8 and a suitable sealing medium such assand l1. Each of the covers l2 and I! are provided with aligned openings[9 and 20 having covers 2| and 22 respectively which may be removed whennecessary to inspect the work, to take the temperature thereof, etc.without removing the larger covers or losing any substantial amount offurnace heat or treating gas. The retort cover I! is also provided witha central staff 23, which may be hollow for the insertion of a pyrometerand or for introducing or venting measured volumes of a treating gaswhen desired, and which serves as a convenient means for lifting'theretort cover off its seat and out of the heating chamber. When used as avent, this stafi or tube 23 besides being provided with means forregulating the volume of spent gas or gases to be vented must beprovided with a check valve to prevent entrance of atmospheric air intothe retort.

The retort l5 may be of any convenient external shape, preferablyhowever it is cylindrical to avoid corner pockets and, in'the embodimentillustrated in Fig. 1, is provided with at least one centrally disposedtubular conduit 24. The tube 24 rests upon an arched plate 25 at thebottom end, and carries at its top end a multi-slotted work supportingbracket member 26. A -plurality of radiating slots 2'! are provided inthe bracket 26, through which the heads of work supporting rods 28 'passandare suspended. Each rod may carry one or more work baskets or asillustrated in Fig. 1, be provided with one or more star-like brackets29 onwhich hollow workpieces, such as those indicated at '30,may bestacked.

The center portion 3| of the main work supporting bracket 26 extendsdownwardly-over'the conduit 24, a distance sufiicient to provide a goodbearing, and has an inwardly extending flange 32 that overlies the endof the tube 24. The very center of the bracket-is apertured at 33 toprovide a passageway for air or gases to or from the interior of thetube '24. The end 24 of the tube 24 may be open to afford 'a'freeflow ofthe gases therethrough, but it is preferred to use a perforated end, asillustrated, to break up and to slightly impede the flow therethrough,for a purpose later to be explained.

The lower end of the central tube 24 is in open communication with apipe line 35 which extends through the bottom 'of the retort, throughthe furnace wall I I, to elements of acirculatory system located at aregion Well removed from the furnace.

The 'pipe '35, however, is surrounded'throughout the major: portion 'ofits'length by a larger second pipe 36, the upper. "endof'which'i'sspaced from the underside of the arched plate 25 and is inopen communication with the chamber 3'! under the plate. The chamber 3'!is divided into at least two substantially separate compartments 31 and3'! by a partition wall 38 which depends from the ceiling of the plate25 to a region near the floor of the retort, leaving, however,sufficient space thereunder for the flow of gases between the pipe 36and the chambers 31* and 31 A similar partition wall 39 extends upwardlyfrom the floor of the chamber 31 and has aninwardly turned flange whichterminates short of the partition wall 38 and spaced from the ceiling ofthe plate 25. The partition 39 thus effectively divides the chamber 31into two further compartments which communicate with each other througha system of restricted passageways of irregular contour. The chamber 3'lalso communicates with the interior of the retort l5 through a-series ofopenings 43 dispersed around the lower margin of the arched plate 25.The plates and 39 are arranged for easy removal and may be held in theirconcentric spaced relation, illustrated in Fig. l, by a series of lugelements 4l.

As illustrated by the arrows a gas or gas mixture flowing upwardlythroughthe space between pipes and 36 is caused to enter the workchamber through a labyrinth of passageways formed by the bafiie membersjust described which have an. impeding .efiect upon the rate of flow ofthe entering air or gases.

The pipe 36-also extends through the bottom of the retort and throughthe wall I l of the furnace and externally communicates with a conduit42 through the medium of a T-member 43 that is sealed at 44 about theinner conduit 35.

The pipe 35 connects with a pipe 45 which, in the system represented byFig. 1, leads to the intake side of the circulating blower or exhaustermechanism 46. The discharge side of the blower mechanism 46 communicateswith the pipe line 42. When the blower is in operation, air or treatinggases are forced through the pipe 42 to the pipe 36 and thence throughthe bailie system situated at the lower end of the work chamber to theinterior thereof. Simultaneously air or gas is drawn 01f at the top ofthe retort through the opening 33 in the work supporting bracket and theperforated end 24* of the central tube, thence downwardly through thetube 24 to the pipe connections 35 and 45. By the piping arrangementjust described, continuous circulation at a moderate rate of anyselected or desired retort atmosphere may be effected.

It will further be observed that the baflle system, comprising plates 25and 39, performs a plurality of functions, one of which is to impede anddisperse the flow of gases entering the work chamber through the pipeline 36, and another of which is to afiord a practical and efficientmeans for heating the gases before they are so dispersed into the workchamber. When the furnace is in operation the bafile plates 25 and 39acquire substantially the same heat as the interior of the retort and asthe entering gases are caused to be repeatedly deflected and agitatedduring their fiow through the reversing passageways, they are caused tobecome cracked or preheated to a temperature approaching that of thework chamber, before they are discharged thereinto. Were the treatinggases to pass through the heating chamber as part of the circulatorysystem they would be at substantially greater heat than the temperatureof the work as they contacted it, and they would blast projecting orthin portions of itcausing uneven heating and warpage which might ormight not be corrected as the mass of the work became heated to thedesired temperature.

The hot gases which are drawn from the top of the work chamberdownwardlythrough pipe 24 and pipe 35 also heat the pipe 35.Accordingly, new air or gases flowing between the walls of pipes 35 and36 extract some of the heat from the outgoing stream of heated gasesflowing through pipe 35 and are caused to become heated to some extentbefore theyreach the main preheating and dispersing system 25, 39 withinthe closed work chamber.

Should it be desirable or should the nature of the work undergoingtreatment require a reversal in the direction of flow of the treatingatmosphere through the work chamber, a reversing valve such asillustrated by the numeral 41 in Fig. 1, may be connected in the lines42 and 45 and set in a position to eifect a reversed flow of theatmosphere. With like effect the blower 45 may be reversible incharacter thereby dispensing with a reversing valve. When the system isoperated reversely, the new gases will enter the work chamber at the topthereof, through the pipe lines 35, 24, and be deflected downwardly.

about the work therein. Simultaneously gases leaving the work chamberwill proceed through the baille system 25, 39 and through the outerconcentrically arranged pipe 36.

During this reversed flow, the gases entering through the inner pipe 35take up part of the heat of the hot gases flowing through the outer pipe36 before entering the central conduit 24, and as the conduit 24 alsowill acquire substantially the same temperature as the work chamber, itprovides a second heating stage for the entering gases before they aredispersed lnto the work chamber.

While a smooth bore tube 23 having a perforated end wall 2 S" has beenfound to produce good results as a preheater for incoming gases, itseffectiveness as a preheater may be increased by the provision ofinwardly extending fins or baffle members 24 such as illustrated in Fig.3.

During normal operation of a closed circulating system of thischaracter, a portion of the air or gas being circulated will be consumedor vented during the treating process and this deficiency may be made upby bleeding into one side of the system, preferably the suction side, afresh supply of the desired gases. In Fig. 1 of the drawings the line 50is connected to a suitable source of supply (not shown) of the gas orgases used during the treating process, which flow through a valve 5|set to pass the amount required into the suction side of the system.

At the pressure side of the system, a combined pressure regulator andtrap 52 may be provided to maintain a given pressure in the system andwhich is also constructed to prevent the entrance of harmful air orgases into the circulatory system. In the present arrangement, thepressure in the system may be adjusted by the regulator 52, and or bythe sand seal Il That is, the seal ll may be constituted to act as atotal seal whereupon the regulator 52 functions exclusively, or it maybe constituted to act as a bleeder and permit a limited outseepage ofgases from the container to occur.

In the event that a reversible circulator 46 is employed, as alluded toabove, a reversing valve similar to the valve 4'! may be connected inthe system between the circulator andthe supply 50, 5| and the regulatortrap 52 "for reversing their connections in correspondence withreversals in the circulator.

In Fig. 2 of the drawings a variant form of circulating system isdisclosed. In this form, the supply line 42 may connect directly withthe source of supply 56 of the gases to be circulated about the work, oras illustrated in Fig. 1, be connectible therewith through the medium ofa reversing valve 41. Also, the exhaust line 45 may connect directlywith a flue or chimney line 45 or connect therewith through theaforesuggested reversing Valve. In the Fig. 2 embodiment of theinvention there is a natural circulation of the atmosphere within theretort and about the work by virtue of the draft created by the chimneysupplemented by the current produced by the pressure of the incominggases. In this system also the gases entering the work chamber passthrough the first and second preheating stages, explained above inconnection with Fig. l, and are gradual- 1y dispersed at a moderate rateto the interiorof the work chamber irrespective of the direction ofmovement of the medium being circulated. It will be understood that thesystem represented'by Fig. 1 is also operable should it be desired toomit the mechanical circulating unit 46 and connect the pipe line 45directly with a chimney, and supply line 50 with the line 42.

In the embodiment of the invention illustrated in the furnace shown inFig. 4, heat is applied to the container H5 in a known way (notillustrated) and the same circulatory and preheating principles for thegas or gases within the container, discussed in connection with Figs.1-3 are, it will be understood, carried out. In this instance, however,the central conduit 24 within the work chamber is made up or constitutedby the work baskets 60 themselves, each of which has an upstanding innerfiange 6| that forms a section of a tube. When the baskets are stackedone upon another, they construct, in the aggregate, a centrally disposedtubular conduit. As illustrated in this figure, each basket 60 ispreferably ring-like in character and has a perforated bottom 62 andimperforate sides BI and 63 provided with top resting flanges 64.

The lowermost basket Si! is arranged to rest upon a ring-like support 65whose top surface 66 is also perforated to permit the flow of gasestherethrough, to or from the work baskets. The outer margin of thesupport 65, which extends to the floor of the retort, forms a continuousclosed ring about the support and effectively confines the flow of thetreating gas through the work baskets and about the workpieces therein.The inner ring portion of the support 65 is provided with an annularflange 61 which fits over a collar 68 on the arched supporting plate 25and eifectively prevents the flow of the gases to whom the conduit 24and the chamber 65 at that juncture.

In this embodiment of the invention, incoming gases are warmed duringtheir flow through the pipe 36, and again heated during their flowthrough the heated baille system 25, 39 "before being discharged intothe chamber 65 The heated gases are then forced upwardly through theperforations in the top 66 of the support and enter the work basketsthru the apertures in their perforated bottoms. The gases continue theirupward progress from basket to basket, as illustrated by the arrows,until they overflow wise forced downwardly through the central tube 24and out through the inner telescoping pipe 35. Pipes 35 and 36 are, itwill beunderstood, connected with units of the circulating system, orcombinations thereof, as explained above in respect to Figs. 1 and 2.

When the direction of flow of the treating atmosphere is reversed, airor gases that are being introduced into the work chamber are initiallywarmed during the flow through'the pipe 35 and again heated during theflow through the central conduit 24 (which may also be provided withbafile plates). The heated treating gases then pass downwardly throughthe work baskets and are exhausted from the bottom of the retort throughthe heme system 25, 39 and pipe 36.

For convenience in'stacking or removing the work baskets, the basketsare provided with a simple form of interlocking connections, such asillustrated at 70, and also with notches H preferably in their outerrims. By engaging a threepronged hook 15 or similar tool, with the rimnotches each basket may beigiven a part turn to lock or unlock it fromthe others. With such an arrangement, one or several baskets may belowered into the retort or removed therefrom in a single operation.

To insure that all unwanted gases are expelled from the system afterreloadingthe Wprk chamher, the circulation of the medium may bestartedafter the work chamber cover is closed on the work but before the workhasreached a temperature such that any entrapped gases would be harmful.

It will be evident from the foregoing that the invention possesses manyadvantages among which may be noted that the user or operator is assuredat all times that the workpieces are being bathed in an atmosphere keptcontinually in a state of motion by means located some distance awayfrom the treating chamber. When distantly located, the several units ofthe circulating means and all moving parts thereof, are not subjectedtoor affected by the heat of the furnace.

from the topmost basket and are drawn or other- Moreover, a circulatorysystem so conceived, is en'tirelyclosed, self-contained, and-certain inits effects upon the work, without regard or consideration to thepossible effect of'the air or gases that may exist in "the furnaceproper. According to thepre'sent invention, no :part of the medium beingcirculated comes in contact with the furnace heating means or with. thedirect heat of the furnace proper. Fumes and .gases given off, by theheating "means and the conditions produced thereby in the heatingchamber of the furnace are definitely excluded from-entering the workchamber and from coming in .contact with the workpieces undergoing aspecific treatment.

Another important advantage'of the invention lies in the fact that thegases entering the work chamber, whether they be wholly or partially newor old, may have the direction of how reversed at will, and irrespectiveof direction of flow are caused to acquire substantially thesametemperature as that .of the work being treated before the gases comeinto contact therewith and in consequence have nochilling efiectthereon. And conversely, by isolating the atmosphere of the heatingchamber I3 from'the work container l5 and'fromithe circulating systemherein proposed, the work undergoing heating and treating isnot blastedby moving currents of a high heat that might be injurious to the workparticularly thinner sections thereof. It will be further seen that thework to be treated in the closed container, in accordance with thisinvention, is not blasted by the in-rush of gas, for the incoming gas iscaused, by reason of the baffle systems arranged at the lower end of thework chamber, as well as at the top end thereof, to be dispersed gentlyinto the work chamber.

The entire system is constructed along simple uncomplicated lines andrenders itself capable of relatively inexpensive manufacture andinstallation in existing furnaces.

Without further analysis, the foregoing will so fully reveal the gist ofthis invention that others can, by applying current knowledge, readilyadapt it for various utilizations by retaining one or more of thefeatures that fairly constitute essential characteristics of either thegeneric or specific aspects of this invention and, therefore, suchadaptations should be, and are intended to be, comprehended within themeaning and range of equivalency of the following claims. v

Having thus revealed this invention, I claim as new and desire to securethe following combinations and elements, or equivalents thereof, byLetters Patent of the United States:

1. A container for maintaining workpieces bathed in a preheatedatmosphere kept in a state of motion, comprising a box section and aremovable cover section, a tube in open communication with the lowerregion of the box section, and a second tube in open communication withthe upper region of the box section, said tubes having portions intelescoping relation with one another; bafflle means in the said boxsection placed in overlying spaced relation with the open end of saidfirst named tube for heating gases introduced through the tube beforesaid gases contact the workpieces; means for heating said container andindirectly the baiiie means therein; and means removed from said boxsection for withdrawing the atmosphere from within the box through thesecond mentioned tube and for returning same to the container throughthe first named tube and the heated bafiie means associated therewith.

2. A furnace in which workpieces may be bathed in a preheated treatinggas or gases during the heating and treating process comprising aheating chamber, a normally closed container within said chamber adaptedto contain the work to be heated and treated, a conduit communicatingwith the interior of said container at the bottom thereof, a secondconduit communicating with the interior of the container at the topthereof, said second conduit extending downwardly through the interiorof the container and having a reduced end portion arranged intelescoping relation with said first mentioned conduit, means forforcing a relatively cool treating gas through one of said conduits intothe container and for withdrawing the eXcess and relatively hot treatinggas from the container through the other of said conduits, thetelescoping relation of said conduits functioning as a heat transferringmeans whereby the treating gas entering the container becomes heatedbefore it contacts the work therein by extracting part of the heat fromthe withdrawn gas.

3. An apparatus for bathing workpieces in a treating gas or gas mixturecomprising a normally closed container adapted to receive the workpiecesto be treated, a conduit communieating with the interior of saidcontainer at one side of the workpieces to be treated, a second conduitleading out of said container and being in open communication with theinterior thereof at the other side of the workpieces to be treated, saidsecond conduit being centrally disposed in said container and extendingthe major portion of the length thereof, and said second conduit alsohaving one end portion thereof arranged in concentric spaced relationwith said first named conduit, means for passing a treating gas throughone of said conduits into said container and for withdrawing the unusedportion of the gas through the other of said conduits, and means forsealing said conduits against flow of the treating gas therebetweenexcept by way of the interior of the container in which the work to betreated is placed.

4. An apparatus useful in the heat treatment of workpieces in acontrolled moving atmosphere comprising an upright container adapted toreceive and enclose the pieces to be heat treated, an upright tubularcolumn located centrally in said container and having its upper end inopen communication with the upper portion of the interior of thecontainer and its lower end extending through the bottom of thecontainer, a second tubular column member also extending through thebottom of thejcontainer and having one end in open communication withthe container interior at the end thereof opposite the open end of saidfirst named column, means and connections exteriorly of the containerfor passing a treating gas through one of said column members into theinterior of the container and through the length of the Work receivingspace in the container interior and for withdrawing the treating gasfrom the container through the other of said conduits, reversing meansoperatively connected with said last named means for selectivelyreversing the direction of flow of the treating gas through said tubularcolumns thereby selectively to reverse the direction of flow of treatinggas through the work container, and means connected with the exhaustingside of the container for injecting a fresh supply of treating gas tomake up for the amount consumed during the heat treatment process.

5. The combination set forth in claim 4 in which baffle means areprovided within the container adjacent the open endof the said conduitsfor effecting a preheating of the treating gas prior to its dischargeinto the zone occupied by the work, said preheating means beingeifective as such when either 'of said column members is functioning asthe gas supplying conduit.

6. A mechanism and system for maintaining workpieces bathed in apreheated atmosphere isolated from the atmosphere of the combustionchamber of a furnace, comprising a normally closed container having awork receiving box section and a removable cover section, a pair oftelescoping conduits for conveying a treating gas into and out of saidcontainer, said conduits passing through the bottom wall of the container and opening into the interior thereof, one of said conduitsopening into the interior of the container at the bottom end, and theother of said conduits extending centrally within the container to theupper and opposite end thereof and at said opposite end opening to theinterior of the container, baflie means also within the containeradjacent the open end of one of said conduits for shielding the workagainst the direct discharge of treating gas from the said conduit andfor heating within the container the treating gas prior to its. contactwith the workpieces; a furnace for heating said container and indirectlythe said baflle means contained within the container; said bafile meansincluding a hollow member having finned portions projecting into thehollow interior adapted and arranged to intercept and deflect theentering gas into heat transfer relation with the walls thereof; andmeans for effecting a flow of. treating gas through one of saidconduits,-

conduit conveying the outflowing gas for injecting a fresh supply oftreating gas thereinto to compensate for the amount consumed during thework treating process.

8. An apparatus for heat treating workpieces combining a furnaceproviding a work heating chamber and means for heating same, a normallyclosed work container within said heating chamber, said container havinga removable cover member at its upper end, a gas inlet and a gas outletconduit opening into said container below the cover member, one of saidconduits opening into said container at the bottom thereof and the otherof said conduits opening into the container interior at the upper regionthere of and both of said conduits passing through the bottom wall ofthe container, gas heating means within the container interior adjacentthe open end of one of said conduits adapted to heat the gas flowingthereinto before the gas enters the work treating area of the saidcontainer, said heating means including a hollow member having finnedportions projecting into the hollow interior adapted and arranged tointercept and deflect the entering gas into heat transfer relation withthe walls thereof; and means at a distance from the furnace forconnecting said outlet conduit with said inlet conduit and for effectinga recirculation of the gas flowing through the outlet conduit back tothe work treating area of said container through said inlet conduit andthe gas heating means associated therewith within the container.

ADOLPH W. MACHLET.

